Sensitive electronic devices, such as flight or engine control computers of aircraft, are accommodated in a space shielded against electromagnetic fields. Conductors are guided to these devices, which conductors come from a space in which strong electrical or magnetic fields of high frequency may occur. The conductors conduct wanted signals. These wanted signals may be analog signals as well as digital impulse sequences. Interfering electromagnetic fields may reach the shielded space through these conductors. Signals which are superimposed over the wanted signals and which drive signal processing into saturation and "clog" the signal processing, may be induced in the conductors. For this reason, filters are provided at the separating wall by which filters such interferences, which may have frequencies up to the range of gigahertz, are eliminated. Therefore, it is known to provide apertures in the shielding separating wall, with one aperture for each conductor. Passage capacitors are located in these apertures. The passage capacitors are soldered or screwed into the separating wall (DE-U-No. 77 29 132, DE-A-No. 1 590 690). With this known method problems arise:
With small devices having a multitude of conductors the separating wall with the multitude of passage filters and plugs is of considerable weight. Passage capacitors having the required capacity values are expensive. Furthermore, supplementary wiring from the entrance plug to the filters, as well as from the filters to the portions of the device arranged in the shielded space is required. Such wiring must be manufactured manually, involving considerable expense.
EP-No. A1-0 181 286 shows a shielded arrangement for interference protection of communication conductors. A double-layer, two-sided printed-board assembly is inserted between an entrance space and an exit space of an interference protection assembly shielded by a bottom and a cover. The printed circuit card comprises instrument ground between the layers. An interference-suppressing network having bleeding resistors, capacitors and coils is provided between input conductors, output conductors and instrument ground. These components are solded, welded or conductingly bonded on or in the printed circuit card.
In this known arrangement, the instrument ground exists only incompletely. The interference-suppressing network is formed by separated components located on the printed circuit card. The incomplete formation of the instrument ground does not offer any protection against extreme high-frequency interference such as those which occur in the range of gigahertz. Also, the interference-suppressing network constructed of separated components loses its filter effect in this high frequency range
DE-No. A1-34 26 278 shows a through plating of a multilayer printed circuit card. The printed circuit card is provided with a shield foil between the layers and a passage hole. The passage hole has a metal lining. The lining is electrically connected to the shield foil. The lining carries an insulating layer on which, in turn, a conductive metal layer is located.
This shielding shall serve to decouple the through plating with respect to adjacent throughplatings. Thus, this printed publication does not relate to the shielding of a space against electromagnetic fields of high frequency. It is true that the lining with the insulating layer and the outer metal layer represents a capacitor, one plate of which, the metal layer, is conductively connected to the shield foil. However, the capacity of a capacitor constructed in such a way is, assuming customary dimensions, too small to permit the shielding of a space against the previously mentioned electromagnetic fields.
CH-A-No. 214 062 shows a passage of a conductor through a shielding wall shielding against high-frequency waves. At the site of the passage, both sides of a metal wall are provided with insulating coatings. The insulating coatings are pressed by metal washers against the metal wall. The washers form capacitors together with the metal wall. The bolts serve as passages.
For each through-going conductor capacitors must be assembled from individual parts which is very expensive in terms of manufacturing engineering.
DD-No. A1-239 916 shows a high-frequency tight assembly having switching circuits mounted on the surface on a multilayer printed circuit card The printed circuit card comprises a "shielding support" in a conductive plane. This shielding support is connected through contact pins to shielding caps covering and shielding the switching circuits. This does not refer to the passage of signal conductors through a shielding separating wall between a space with high-frequency electromagnetic fields and a space which should be protected against such fields.
EP-No. B1-0 162 146 shows a shielded cabinet in which filter assemblies are inserted into a mounting wall. DE-No. U1-83 09 875.5 relates to a printed circuit plate having partially parallel strip conductors, a ground conductor being arranged between these strip conductors for their capacitive decoupling. E-No. A2-0 264 105 relates to a method for manufacturing multilayer printed circuit cards in which at least one layer is formed by a metal plate.